The present invention relates to a process for the preparation of glycidylesters of branched carboxylic acids.
More in particular the present invention relates to a multistep process for the preparation of glycidylesters of xcex1,xcex1xe2x80x2-branched dicarboxylic acids.
Glycidylesters of xcex1-branched carboxylic acids are useful for the preparation of epoxy resins, acrylic polyester resins and alkyd resins, either directly or via intermediate products such as adducts with (meth)acrylic acid amines, polyols and polyacids, or as reactive diluents for the preparation of thermoset acrylic, epoxy, polyester and/or urethane paints and coatings.
Glycidylesters of mono, xcex1-branched carboxylic acids and their method of preparation are disclosed in U.S. Pat. No. 3,075,999, 3,178,454, 3,275,583 and 3,397,176.
In particular diglycidylesters of xcex1,xcex1-branched aliphatic dicarboxylic acids and diglycidyl esters of xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-branched aliphatic dicarboxylic acids are known from NL-286209A, DT-OL 1942836A, U.S. 3,629,295A, GB-1,360,811B, GB-1,360,812B, GB-1,360,813B, EP-0518408B1 and from WO98/52932.
In the majority of said publications, said glycidyl-esters are made by reacting an alkali salt of the carboxylic acid with a halo-substituted monoepoxide such as an epihalohydrin, e.g., epichlorohydrin (1-20 molar excess). The mixture is heated (50-150xc2x0 C.) in the presence of a catalyst forming glycidylester plus alkali salt and water. The water and excess epihalohydrin are removed by azeotropic distillation, and the salt by-product, e.g., NaCl, is removed by filtration and/or washing. The glycidylesters can also be made by reacting the carboxylic acid directly with epichlorohydrin under similar process conditions. The chlorohydrin ester intermediate formed during this reaction is subsequently treated with an alkaline material, e.g., sodium or potassium hydroxide, which yields the desired glycidylester. By-product salt is removed by washing and/or filtration, and water is removed by drying.
However, said conventional processes have appeared to provide glydicylesters which showed unattractive halogen contents, making them not applicable for highly sophisticated coating applications on metal substrates, for which high corrosion resistances are required.
On the other hand the economics of modern coating industries, in which an important proportion of the total output of said glycidylesters is used as starting material, required lower prices per unity active product (i.e. higher EGC values) and related therewith lower manufacturing costs of said glycidylester starting materials.
In the more recent publication WO98/52932 diglycidylesters of a specific group of 3,4,5,6-alkyl-substituted cyclohexane-1,2-dicarboxylic acid were prepared by means of a Diels-Alder reaction of maleic anhydride and specific dienes, such as allo-ocimene.
However again, the products of such a preparation were characterized by relative low EGC values (as compared to the theoretical yield) and a relatively bad efficiency.
It will be appreciated that for particular application of said glydicylesters in clear coatings, there has been developed a growing need for colourless and colour stable products.
It is generally known that mono- and diglycidylesters are thermally and chemically reactive molecules, which cannot be easily recovered from initially prepared, coloured crude glycidylesters.
It has been found that standard atmospheric distillation techniques usually increase the amount of by-products as well as the degree of colour of the esters. It is known that this increase in colour is caused by the reaction at elevated temperatures, as encountered during distillation, of the glycidyl functionality present in the desired product with functionalities present in the by-products, thereby forming additional by-products, which are not separable from the glycidylester and which are extremely sensitive to discoloration upon heating.
It will be appreciated that there is still a need for an improved manufacturing process for glycidylesters of xcex1,xcex1xe2x80x2-branched dicarboxylic acids, and in particular of xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-branched aliphatic dicarboxylic acids, which may lead to diglycidylesters of the performance of the product aimed at, and at a lower cost price.
An object of the present invention therefor is to provide a process for the manufacture of glycidylesters of xcex1,xcex1xe2x80x2-branched dicarboxylic acids, with significantly lower halogen content (i.e. total halogen content and hydrolyzable halogen content), heat stability and colour stability and/or higher purity, which must be reached at a reduced cost price per product unit.
As a result of extensive research and experimentation, such a process has been surprisingly found now.
Accordingly, the invention relates to a process for the manufacture of diglycidylesters of xcex1,xcex1xe2x80x2-branched dicarboxylic acids, comprising
(a) the reaction of the xcex1,xcex1xe2x80x2-branched dicarboxylic acid with a halo substituted monoepoxide such as an epihalohydrin (e.g. epichlorohydrin) in a 1.1-20 acid equivalent ratio relative to the xcex1,xcex1xe2x80x2-branched aliphatic dicarboxylic acid and preferably in acid equivalent ratio of 3-20, optionally in the presence of water and water-miscible solvent and preferably an aqueous alkanol as solvent, and in the presence of a catalyst in an amount of at most 45 mol % of the acid equivalent amount of the xcex1,xcex1xe2x80x2-branched aliphatic dicarboxylic acid, and preferably at most 20% and more preferably of at most 10%, at a temperature in the range of from 30 to 110 (and preferably from 65 to 95xc2x0 C.), during a period in the range of from 0.5 to 2.5 hr,
(b) addition of alkali metal hydroxide or alkali metal alkanolate up to an acid equivalent ratio as to the xcex1,xcex1xe2x80x2-branched aliphatic dicarboxylic acid in the range of from 0.9:1 to 1.2:1 and preferably from 0.95:1 to 1.10:1 and reaction at a temperature of from 0 to 80xc2x0 C. (and preferably from 20 to 70xc2x0 C.),
(c) distillation of the obtained reaction mixture to remove the excess halo substituted monoepoxide and the solvent and water formed, and
(d) removal of alkali metal halide salt, preferably by washing the obtained diglycidylester with water mixed with an inert organic solvent, after optionally treating the residual product with a concentrated aqueous alkali metal hydroxide solution, in order to complete the dehydrohalogenation (and preferably a dehydrochlorination).
It will be appreciated that the diglycidylester obtained after step (d), can be dried in addition e.g. by distillation or treating with water absorbers.
The process according to the present invention can be carried out either as batch process or as a continuous process. The process preferably uses xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-branched aliphatic dicarboxylic acids, containing from 8 to 24 carbon atoms.
Of particular interest are diglycidylesters of xcex1,xcex1xe2x80x2-branched aliphatic carboxylic acids represented by the formula: 
wherein R1, R2, R3, R4, R5, R7, R8, R9, R11, R12, R13 and R14 may be the same or different and each may represent hydrogen or a lower alkyl group containing from 1-4 carbon atoms and preferably 1 or 2 carbon atoms, wherein R6 and R10 may be the same or different and each may represent an alkyl group containing from 1 to 10 carbon atoms and preferably from 1 to 4 or a cycloaliphatic ring having 5 or 6 carbon atoms, optionally substituted with one or more lower alkyls, and wherein the total carbon atoms in the diacid part of the diglycidyl esters of formula 1 are in the range of from 8 to 24 carbon atoms, and preferably from 10 to 14 carbon atoms, and wherein n is an integer in the range of from 0 to 8, and preferably from 2 to 6.
Preferred diglycidylester of dicarboxylic acids of formula I are those wherein R5, R6, R9 and R10 are methyl and/or ethyl groups, wherein R7 and R8 are hydrogen, and n is in the range of from 2 to 6.
With the term xe2x80x9calkanolxe2x80x9d as used throughout this specification are meant mono-alkanol as well as polyalkanols, such as glycols. More preferably as alkanol isopropyl alcohol is used.
The amount of alkanol in the aqueous alkanol solution is preferably at least one mole alkanol per mole dicarboxylic acid.
The preferred reaction time in step (a) is in the range of from 0.9 to 1.5 hours.
The catalyst to be used in step (a) may be selected from alkalimetal hydroxides, alkalimetal carbonates, alkaline earth hydroxides, alkalimetal or alkaline earth metal alcoholates of the formula Xn+(ORxe2x88x92)n, wherein X represents the alkali metal or alkaline earth metal ion and R represents C1-C12 alkyl, n represents the valence of the metal ion, or ammonium salts and in particular hydroxides or halides of the formula R15R16R17R18N⊕Yxe2x88x92, wherein R15, R16 and R17 independently of each other may represent an alkyl group having from 1 to 16 carbon atoms, which optionally may be substituted with one or more hydroxyl groups, wherein R18 represents an alkyl group having from 1 to 16 carbon atoms, phenyl, benzyl, or cycloalkyl of 5 or 6 carbon atoms, and wherein Y represents hydroxyl or halogen.
Another suitable group of basic catalysts for step (a) is formed by phosphonium halides of the formula R20R21R22R23P⊕Zxe2x88x92, wherein R20, R21, R22 and R23 independent of each other may represent monovalent hydrocarbon groups. Preferably R20, R21 and R22 are alkyl, cycloalkyl, aryl, aralkyl, having at most 25 C-atoms and more preferably having at most 18 C-atoms, such as phenyl, butyl, octyl, lauryl, hexadecyl or cyclohexyl. R23 is preferably an alkyl group of from 1 to 10 C-atoms and more preferably of from 1 to 4 and wherein Z is a halogen, such as chlorine, bromine or iodine.
Alkalimetal hydroxides or alkali metal alkanolates having from 1 to 6 carbon atoms are most preferred as catalyst in step (a).
The alkalimetal hydroxide which is used in step (a) may be selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide, of which sodium hydroxide or potassium hydroxide is more preferred. It will be appreciated that in step (b) only relatively strong and water-soluble metal hydroxides or metal alcoholates have to be used, whereas weaker, less water-soluble metal hydroxides or carbonates are less preferred.
It will be appreciated that the specified molar ratios in step (b) will be constituted by additions of alkali metal hydroxides or alkali metal alkanoates on both steps (a) and (b).
With the term xe2x80x9cdistillationxe2x80x9d used in step (c) is meant removal of the light fractions from the initially obtained reaction mixture (which is indicated in the art as xe2x80x9ctoppingxe2x80x9d).
In addition, according to a preferred embodiment of the present invention the brine formed in step (a) can be completely or partially removed before entering step (b).
The alkali metal hydroxide or alkali metal alkanolate which is used in steps (b) and (d) are preferably selected from sodium hydroxide, sodium alkanolate having from 1 to 6 carbon atoms, such as sodium isopropanolate, lithium hydroxide or lithium alcoholate. Most preferably sodium hydroxide or sodium alkanolate having from 1 to 6 carbon atoms is used.
Preferably for step (b) sodium hydroxide is used in an aqueous solution of a concentration of from 10 to 60% by weight and more preferably from 20 to 50% by weight.
It will be appreciated that according to the process of the present invention a drying cq. solvent removal step can take place after the washing in step (d), if desired.
It will be appreciated that the process of the present invention can be applied on sole xcex1,xcex1xe2x80x2-branched aliphatic dicarboxylic acids or on mixtures thereof.
Mixtures of diglycidylesters of xcex1,xcex1xe2x80x2-branched aliphatic dicarboxylic acids are produced, when starting from technical grades of commercially available compositions of xcex1,xcex1xe2x80x2-branched aliphatic dicarboxylic isomers.
Examples of such acids are 2,4-dimethylglutaric acid, 2,5,5-trimethyladipic acid, 2,2,4,4-dimethylglutaric acid, 2,2,5-trimethyladipic acid, 2,3-dimethylsuccinic acid, 2,2,3,3-tetramethylsuccinic acid, 2,2,6,6-tetra-methylpimelic acid, 2,5-dimethyladipic acid, 2,2,5-tri-methyladipic acid, 2,2,5-trimethyl-5-ethyladipic acid, 2,9-dibutylsebacic acid, 2,2,9,9-tetramethylsebacic acid, 2,2,7,7-tetramethylsuberic acid, 2,2,6-trimethyl-6-ethylpimelic acid and 2,2,5,5-tetramethyladipic acid.
Preferably di-carboxylic acids having 8 to 14 carbon atoms are used as starting material.
It will be appreciated that according to the more preferred embodiments of the process of the present invention step (d) will be carried as anhydrous as possible, i.e. using highly concentrated sodium hydroxide solutions e.g. up to 55 wt %.
It has surprisingly been found, that the process of the present invention can provide very pure glycidylesters of xcex1,xcex1xe2x80x2-branched aliphatic dicarboxylic acid, i.e. showing contents of heavier byproducts less than 6 wt % and preferably less than 5 wt. and more preferably less than 4 wt %, which show the desired reduced initial colour, the improved colour stability after extended periods of storage, which surprisingly show a low total halogen content and in particular total chlorine content (e.g. xe2x89xa61400 mg/kg) and a low hydrolyzable halogen, and in particular chlorine, contents (e.g. 450 mg/kg), and which do not need tailing by distillation for purification, while the process can be further characterized by a very high conversion and selectivity of the halo substituted epoxide with reference to the desired glycidylester. Moreover a very efficient and easy phase separation could be obtained in the last recovery step.
More in particular it could not be expected by a person skilled in the art that the presence of a base in steps (b) and (d) does not significantly hydrolize the present, just formed glycidylester.
It will be appreciated that preferably an alkanol will be used which enables the dissolution of a sufficient amount of base into the organic phase, whereas on the other hand the total water content in the reaction mixture of step (a) is to be kept in the range of from 4 to 13 mol/mol acid.
The process of the present invention is more preferably carried out, starting from xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-branched aliphatic dicarboxylic acids, containing from 8 to 14 carbon atoms in the acid moiety, and most preferably from 10 to 14 carbon atoms.
According to a preferred embodiment of the process of the invention, the initially prepared diglycidylester is washed in step (d) with a mixture of water and solvent which facilitates the phase separation aimed at. More preferably a weight ratio of solvent and diglycidylester is from 20:80% to 80:20%.
It has been found that the water content in step (d) should be as low as possible to avoid hydrolysis of the diglycidylesters to be formed. Preferably a highly concentrated aqueous solution of alkali metal hydroxide is used in step (d).
For the same reason the hydrolysable chlorine content after step (b) should be minimized ( less than 25000 mg/kg). A too high level can be reduced by known methods such as an increase of the amount of base used or by a reduction of the reaction temperature in step (b).